Output circuit question

[Mark Atterbury]

I have been building my MS-II from the DIY autotune kit. I am using the Jim Stim to validate and test at each test point in the assembly instructions. The code version is something like 2891?

Everthing tested fine until the output circuit (final validation test). I have gone back through the steps and verified components and polarity - everthing looks good. I am building for an EDIS so I don't have the components for the high current drive installed (i.e. Q16, R43, etc). I am also building for a stepper IAC.

The initial test checked good with the RPM and fuel pump light. The Fidle light would flicker inconsistently (not too worried since I will use IAC). However, all three LEDs on the MS board (D14, 15 and 16) were constantly illuminated.

Once I started to program with Megatune, other weird stuff occurred. However, all the gauges look fine in either display mode in Megatune. They respond as anticipated to the pots on the Jim Stim.

Here are the current symptoms:
1. All three LEDs on the MS are constantly on.
2. The Fuel pump LED on the Jim Stim no longer is lit. There is -5V measured between the FP pin on the 19 pin header and ground. I would think this should be +5V.
3. The Fidle LED on the Jim Stim flickers

All else seems to be working. I reloded the S19 and the .msq file to the MS. No change.

Any idea where I should look next? Am I missing a jumper somewhere? A bad Diode? Any help would be apreciated.

Mark

[Matt Cramer]

I have been building my MS-II from the DIY autotune kit. I am using the Jim Stim to validate and test at each test point in the assembly instructions. The code version is something like 2891?

Everthing tested fine until the output circuit (final validation test). I have gone back through the steps and verified components and polarity - everthing looks good. I am building for an EDIS so I don't have the components for the high current drive installed (i.e. Q16, R43, etc). I am also building for a stepper IAC.

The initial test checked good with the RPM and fuel pump light. The Fidle light would flicker inconsistently (not too worried since I will use IAC). However, all three LEDs on the MS board (D14, 15 and 16) were constantly illuminated.

Once I started to program with Megatune, other weird stuff occurred. However, all the gauges look fine in either display mode in Megatune. They respond as anticipated to the pots on the Jim Stim.

Here are the current symptoms:
1. All three LEDs on the MS are constantly on.

Do they turn off if you remove the MS2 daughter card?

2. The Fuel pump LED on the Jim Stim no longer is lit. There is -5V measured between the FP pin on the 19 pin header and ground. I would think this should be +5V.

This would normally be 5 volts from the FP pin to ground if the fuel pump is off and 0 volts if it's on. Not sure where a minus voltage could come from unless your red probe is on the ground pin.

3. The Fidle LED on the Jim Stim flickers

How is your idle control set up?

[Mark Atterbury]

Thanks for the quick response.

The MS LEDs stay on if the daughter card is removed.

I re-checked the voltage from the 19 pin FP pin to ground (Jim Stim)- it now reads +3.5V. I swear it was -5V earlier, but...

The Fidle pin to ground also reads +3.5V and drops to +3.0V as the light flickers on.

I validated that the LEDs on the Jim Stim are working correctly. I really think there is some voltage issue somewhere. The LEDs on the MS lead me to think it is there and not on the Stim.

Now after fiddling with them for the evening the INJ1 LED on the Stim is on constantly.

The idle settings are:
IAC stepper always on
Time step size 2.5
Accel step size 0
Min # steps to move 1
Start value 160
Cranking pos 100
Crank to run taper 5
Hysteresis 5.0
Cold temp -40
cold posn 120
cold taper 40

Any ideas where to check? If it wasn't for the LEDs on the MS, I would suspect that the stim is the problem. Let's Try and solve that first.

Thanks for your help.

Mark

[Matt Cramer]

Any ideas where to check? If it wasn't for the LEDs on the MS, I would suspect that the stim is the problem. Let's Try and solve that first.

Thanks for your help.

Mark

Ok, so the LEDs are on when the daughter card is removed. First check the transistors that drive them, make sure they're not in backwards or shorted out.

[Mark Atterbury]

I am assuming that Q6, 7 and 8 are the tansistors driving the LEDs. I am confident that they are instaled the correct way around (flat side matching the silk screen). I have visually checked that they are not shorted due to solder bridges, but my eyes are not as young as they once were. I'll double check tonight with the "bright light" and confirm with you tomorrow.

If the transistors check out OK, what is the next step in the chain?

Thanks,
Mark

[Mark Atterbury]

Good morning Matt,

I examined all the transistors, and they are all installed in the correct orientation. There are no visible solder bridges. Is there any way to verify that they are good with the multimeter?

I wish I had a deeper understanding of the electronics - sometimes you are forced to get your wish. What is the next step?

Thanks
Mark

[a73camaro]

With a multimeter set on ohms, measure the resistance between each transistor leg. If there is a solder bridge, it will be pretty obvious on the meter.

[Mark Atterbury]

OK - so if I measure the resistance across each of the legs of the small transistors when installed on the board I should get infinite resistance? (no needle movement on my multimeter when set to measure ohms). Just want to make sure that there are no back paths for the current to flow, thereby giving a reading on the meter. Is this true for all the transistors, or only the ones driving the LEDs?

I checked all the small transistors and only a few of them have infinite resistance between the legs. None of them have infinite resistance between all of the legs.

I thought I was doing well with the solder, and there are no visible bridges on the bottom of the board, but maybe they are bridged at the top side and I can't see them because the component body is in the way?

Hope that this is the issue, but want to make sure my measurements are correct before I attempt to remove all of the transistors (yuck)

Thanks for the help,
Mark

[a73camaro]

On any meter, a short will show up as zero ohms. When testing a component on a circuit board, the meter can be “back feeding” other components that are connected in parallel to the item being tested. Also the transistor doesn't have infinite resistance; if you test from the base to the emitter you would see results like testing a diode. So you may see a 1000 ohms, but you may see infinite. Just look for a dead short.